Magnetically restorable high speed print hammer

ABSTRACT

An electromagnetic print hammer comprises a magnetic core structure having a magnetic core with an armature movable between one flux path and another flux path. Means are provided for producing a magnetic flux in said core structure and control windings are energized to switch the flux from said one to said another flux path causing the armature to change position.

United States Patent [191- Kroft et al. Jan. 16, 1973 [54] MAGNETIC ALLY RESTORABLE'HIGH 3,609,609 9/l97l Bertazzi ..335/279 X SPEED PRINT HAMMER [75] Inventors: John D. Kroft, Endwell; Joseph P. gummy s qf zfi g g s V l Pawletko, Endwe"; Francis E. ttorney am m ancm an rancis l0 ma Peters, Endwell; Carl T. Young, s, .7 s e w he Binghamton, all of NY. 57 ABSTRACT [73] Assignee: International Business Machines An electromagnetic print hammer comprises a Corporatmn, Armonk netic core structure having a magnetic core with an [22] Fil April 15, 1971 armature movable between one flux path and another flux path. Means are provided for producing a mag- [211 Appl' 134354 netic flux in said core structure and control windings are energized to switch the flux from said one to said [52] US. Cl. ..335/266,' 101/93 C another flux path causing the armature to change o i [51] Int. Cl. ..H01f 7/08 tion. [58] Field of Search ..335/227, 266, 268, 276, 279; 101/93 C [56] References Cited 10 Claims, 5 Drawing Figures UNITED STATES PATENTS 3,305,809 2/1967 Ludwig ..335/276 X WWII SHEET 1 0F 2 JOHN D. KROFT JOSEPH P. PAWLETKO I FRANCIS E. PETERS n FIG. 1 CARL T. YQUNG MAGNETICALLY RESTORABLE HIGH SPEED PRINT HAMMER CROSS-REFERENCE TO RELATED APPLICATION FIELD OF INVENTION This invention relates generally to magnetic actuators and it has reference in particular to a magnetically operated and reset print hammer.

DESCRIPTION OF THE PRIOR ART Heretofore, electromagnetic actuators for printers have been designed either as separate devices connected to a print hammer by a pushrod or the like, as in the US. Pat. No. 3,241,480, which issued on Mar. 22, 1966, to James M. Cunningham, or as simple armature type actuators impacting a print hammer as in US. Pat. No. 3,507,213 to R. Derc, which issued Apr. 21, 1970.

SUMMARY OF THE INVENTION Generally stated, it is an object of the invention to provide a new and improved electromagnetic print hammer for a printer.

More specifically, it is an object of the invention to provide an electromagnetic print hammer in which switching of magnetic flux from one path to another causes operation of the actuator or print hammer.

Another object of the invention is to provide an electromagnetic print hammer in which an armature rotatably supported between pole pieces of a stationary magnetic core is actuated by transferring magnetic flux between the pole pieces from one flux path having a radial air gap to another flux path having a peripheral air gap.

Yet another object of the invention is to provide an electromagnetically operated print hammer, which is operated by switching magnetic flux from a constant length air gap to a linearly variable air gap.

It is also an important object of the invention to provide for switching magnetic flux from a radial air gap defined by associated toothed core and armature surfaces to a peripheral air gap defined by core and armature portions disposed in substantial abutting relation.

Yet another object of the invention is to provide an electromagnetically operated print hammer, wherein operating windings mounted on portions of pole pieces on either side of a rotatable armature cause a transfer of magnetic flux from a radial toothed air gap between the pole pieces to a linear air gap between the core and armature portions which move towards each other along a path of decreasing length.

Still another object of the invention is to provide an electromagnetically operated rotatable print hammer having both drive and impact portions, and a detent and restoring portion.

Still another important object of the invention is to provide a print hammer having a rotary impact member with detent teeth and a linear drive air gap.

It is also an important object of the invention to provide an actuator having an armature and a stationary magnetic core structure with projecting pole pieces providing a peripheral or linear air gap path for an operating magnetic flux, and a corresponding curved radial air gap defined by corresponding curved armature and core toothed portions wherein the toothed portions are displaced relative to each other in the operated position so as to exert the maximum restoring torque.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawing.

DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a schematic showing in side elevation, partly in section and partly broken out, of an electromagnetically operated print hammer structure embodying the principal features of the invention,

FIG. 2 is a schematic showing in front elevation of the print hammer structure of FIG. 1,

FIG. 3 shows curves illustrating the relative drive force and restore force acting on the armature of the actuator in different positions,

FIG. 4 shows flight time and print force curves for the actuator of FIGS. 1 and 2 for different values of air gap, and

FIG. 5 shows curves illustrating the timing of drive and damping pulses applied to the print hammer relative to the hammer displacement.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring particularly to FIG. 1 of the drawing, it will be seen that the Actuator 10 comprises generally a stationary magnetic core structure having Upper and Lower Core Members 11 and 12 with a Central Core Member 14 positioned therebetween. The Core Members ll, 14 and 12 are connected by Core Members 13 and 15, which complete the magnetic circuit. The upper and lower core members are provided with salient Pole Pieces [6 and 18 having Operating Windings 20 and 22 thereon, respectively. The Intermediate Core Member 14 may comprise a plurality of laminations having upwardly and downwardly disposed salient Pole Pieces 24 and 26 having Operating Windings 28 and 30, respectively. Adjacent the Pole Pieces l6 and 24 and on opposite sides thereof are provided curved or peripheral portions defined by a plurality of spaced Teeth 32 and 33, respectively. Likewise, the Pole Portions 18 and 26 have similar curved surfaces defined by spaced Teeth 34 and 36, respectively.

Armatures 38 and 40 are rotatably supported by means of Pivot Shafts 42 and 44, respectively, and Support Arms 46 and 48, which are respectively secured by means of Pins or Rivets 50 and Screws 52 to support means connecting the Core Members ll, 14 and 12, such as a body of molded Polyurethane Plastic 54 which may be bonded to the core members. The Armatures 38 and 40 are provided with projecting Pole Portions 58 and 60, and 62 and 63, which are positioned so as to move into abutting relation with the corresponding Pole Pieces 16, 24, 18 and 26, respectively, when the Arrnatures 38 and 40 are rotated about their Pivots 42 and 44 in counterclockwise and clockwise directions, respectively. The Armatures 38 and 40 are providedwith corresponding toothedPortions 64, 66, 68 and 70 disposed in cooperative relation with the toothed peripheral Portions 32, 33, 34 and 36 of the Core Members 11, 14 and 12, respectively. The Armatures 38 and 40 are provided respectively with depending and upstanding Arm Portions 72 and 74 having Hammer Faces 76 and 78 for impacting a Document 80 and Ribbon 82 against a Type Element 84, which may be mounted on a type chain, belt or the like for movement past a print position. A Residual 86 of non-magnetic or plastic material such as Polyurethane may be secured to one or both surfaces of the Pole Pieces 16, 18, 24 and 26 to prevent sealing of the armature to the pole pieces when operated. Resilient stops may be provided comprising Flat Springs 88 and 89 with Rubber Bumpers 90 and 91, respectively. The Springs 88 and 89 may be secured in Slots 92 and 93 and adjusting Screws 94 and 95 may be provided for adjusting the rest positions of the Armatures 38 and 40.

It will be seen that the Armature 38 is shown in'the operated position with the projecting Pole Piece 58 substantially abutting the Residual 86 of the salient Pole Piece 16 of the stationary Core Member 10. In this position the Hammer Face 76 is impacting the Document 80 and Ribbon 82 with the Type Member 84 for printing. In this position the Teeth 64 and 66 are in offset relation with their corresponding toothed Portions 32 and 33 of the Core Members 1 l and 14, overlapping only about 20-40 percent so as to obtain sufficient restore force. The Armature 40 is shown in the nonoperated position with the Pole Pieces 62 and 18 and 63 and 26 separated their maximum amount. In this position the Teeth 34, 36, 68 and 70 are substantially in alignment.

In the position shown for the Armature 40, windings on the Core Members and 12 represented by the Winding 17 on Core Member 12 provide a detentmagnetic flux (b2 which normally traverses the radial air gap between the Teeth 36 and 70 and 68 and 34 in sequence. When the Operating Windings 22 and 30 are pulsed, a principal part of the magnetic flux (#2 is switched from the radial path between the spaced peripheral teeth and instead traverses the peripheral or linear air gap path designated by the flux 411 between the Pole Pieces 18, 62, 63 and 26, exerting a drive force on the Armature 40. to operate it in a clockwise direction so as to close up the peripheral or linear air gaps between the pole pieces. When the Armature 40 moves to the operated position, the Hammer Face 78 impacts the Document 80 and the Pole Pieces 62 and 18 and 63 and 26 will be substantially in abutting relation with the Residual 86 as shown for the Armature 38. In this position the spaced Teeth 68 and 70 will have, moved'out of alignment with the corresponding Teeth 34 and 36 of the core members and will be in the offset position as shown for the Teeth 64 and 66 of the Armature 38, in which they exert sufficient restore force to return the Armature 40 to the original position as soon as the drive pulse to the Windings 22 and 30 is terminated.

It will be seen that the Actuator 10 is a rotary device with two flux paths, one through the large drive air gap between the Pole'Pieces l6 and 58, for example; the other through a relatively short radial gap or variable reluctance path between the spaced Teeth 32 and 64. With a plurality of actuators arranged in side-by-side relation, as shown in FIGS. 1 and 2, a common Winding l9 encompasses the Upper Leg Portions l1 and a common Winding 17 encompasses the Lower Leg Portions 12 of all actuators to provide a steady state magnetic field which forces all units to line up for minimum reluctance values, whereas separate Operating Windings and 28 are provided on the salient Pole Pieces l6 and 24 of each of the actuators. In a nonoperated position approximately 10 percent of the main flux produced by the Winding-11 fringes through the air gap between the salient Pole Pieces 16 and 58, which assures a minimum of initial motion delay, while at the same time minimum interaction occurs between adjacent paths. Energization of the Windings 20 and 28 provides sufficient magnetomotive force to cause the magnetic flux to switch paths and a rotational force to develop. This causes the Armature 38 to rotate, and as it rotates, the teeth of the Restore Paths 32-64 and 33-66 saturate, diverting most of the flux into the main air gap between the salient Pole Pieces 16-58 and 60-24.

Measurements made show that the following conditions occur:

Initial flux in the restore path z 2,000 lines.

Initial flux in the drive path 300 lines.

Immediately before motion starts Restore Field 800 lines, Drive Field 1,650 lines.

When Forward Stroke completed, Restore Field 350 lines, Drive Field 2,300 lines. These results were obtained with approximately 880 ampere turns for the Hold Windings 17-19, and 1,800 ampere turns for the Drive Windings 20, 28, 22 and 30.

As shown in FIG. 3, as motion of the armature proceeds, the Drive Force increases, following the path A, and the Restore Force decreases, following path B. Drive current can be cut off much sooner than the Stroke Completion time, since while the current is collapsing, the reluctance of the Drive Gap 16-58 decreases keeping the Drive Force positive and almost constant. Once impact occurs very little rebound force is required to develop a positive restoring force't'o follow the path C. The relationships between the input pulse width and the energy available is shown in FIG. 4. This also shows the flight time variations'as a function of the drive pulse and the length of the stroke.

In one embodiment the armature had a radius at the peripheral tooth portion of approximately 0.687 inches, the width of the teeth was approximately 0.047 inches with the slots having a width-of approximately 0.0662 inches. The thickness of the armature is approximately 0.094 inches so that the actuators or print hammers may be arranged on 0.10 inch centers. The gap between armature and core member piece ison the hammer actuators embodying the invention have been operated to provide a print force of approximately 75'230,000 ergs with a response time on the order of 0.6 to 1.1 Ms, a settling time of 1.9 to 3 Ms and a usable stroke of 0.035 to 0.050 inches. As shown in FIG. 5, drive and damping pulses a and b can be provided in spaced relation to give a displacement curve c.

it will be seen from the above description and the accompanying drawing that the print hammer actuator of the present invention provides a simple and efficient mechanism which requires no restore springs. Only one moving part per unit is necessary, which part directly impacts to provide the printing force. This enables high speed operation with relatively low drive power and electrical damping, if desired.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and the scope of the invention.

What is claimed is:

.1. An electromagnetic actuator comprising,

stationary core means of magnetic material having spaced apart pole pieces,

an armature rotatably positioned between said pole pieces having an actuator extension disposed to be actuated by rotational movement of said armature and having spaced apart projecting portions disposed in predetermined spaced relation with portions of said pole pieces to move into substantially abutting relation therewith upon rotation of said armature,

means including a winding on said core means operable to produce a magnetic flux along one path between said armature and said pole pieces to effect biasing of said armature to a normal position, and

means including winding means on said pole pieces operable when energized to switch said magnetic flux to another path between said armature and said projecting portions to cause rotary movement of said armature away from said normal position.

2. The invention as defined in claim 1 characterized by said projecting armature portions and said stationary magnetic core means having surfaces defining substantially peripheral air gaps.

3. The invention as defined in claim 2 characterized by said stationary magnetic core means having additional portions on opposite sides of said pole pieces with at least one projecting tooth, and said armature having a corresponding tooth in at least partially offset relation with its associated magnetic means tooth in line (6) 4. The invention as defined in claim 3 characterized by said additional portions of the core means and said armature each having a plurality of spaced apart teeth which are arranged along spaced apart corresponding curved surfaces defining a constant length radial air gap.

5. The invention as defined in claim 4 characterized by a magnetic flux path through said peripheral air gap having a reluctance greater than five times that of the flux path throu it said radial air gap in normal position.

6. The lnven ion as defined in claim 3 characterized by said core means having one winding thereon to normally provide a magnetic flux across both said radial air gaps to bring said armature and core means teeth into aligned relation and another winding on said pole pieces to produce a magnetic flux across said peripheral air gaps alone and switch magnetic flux from said radial to said peripheral air gaps.

7. The invention as defined in claim 6 characterized by at least one of said projecting armature portions being disposed to so move relative to its associated pole piece as to reduce the overlapping area of said projecting portion and said pole piece as the length of the air gap therebetween diminishes.

8. The invention as defined in claim 6 characterized by a plurality of said core means and associated rotatable armatures being positioned in side-by-side relation with the actuator extensions disposed alternately in opposed relations.

9. The invention as defined in claim 8 characterized by the winding producing magnetic flux through both the radial and peripheral air gaps being common to a plurality of said core means in side-by-side relation, while the windings producing magnetic flux across only the peripheral air gaps are individual to each armature.

10. The invention as defined in claim 9 characterized by said plurality of magnetic core means being joined by a molded plastic means bonded to all of said core means. 

1. An electromagnetic actuator comprising, stationary core means of magnetic material having spaced apart pole pieces, an armature rotatably positioned between said pole pieces having an actuator extension disposed to be actuated by rotational movement of said armature and having spaced apart projecting portions disposed in predetermined spaced relation with portions of said pole pieces to move into substantially abutting relation therewith upon rotation of said armature, means including a winding on said core means operable to produce a magnetic flux along one path between said armature and said pole pieces to effect biasing of said armature to a normal position, and means including winding means on said pole pieces operable when energized to switch said maGnetic flux to another path between said armature and said projecting portions to cause rotary movement of said armature away from said normal position.
 2. The invention as defined in claim 1 characterized by said projecting armature portions and said stationary magnetic core means having surfaces defining substantially peripheral air gaps.
 3. The invention as defined in claim 2 characterized by said stationary magnetic core means having additional portions on opposite sides of said pole pieces with at least one projecting tooth, and said armature having a corresponding tooth in at least partially offset relation with its associated magnetic means tooth in line (6)
 4. The invention as defined in claim 3 characterized by said additional portions of the core means and said armature each having a plurality of spaced apart teeth which are arranged along spaced apart corresponding curved surfaces defining a constant length radial air gap.
 5. The invention as defined in claim 4 characterized by a magnetic flux path through said peripheral air gap having a reluctance greater than five times that of the flux path through said radial air gap in normal position.
 6. The invention as defined in claim 3 characterized by said core means having one winding thereon to normally provide a magnetic flux across both said radial air gaps to bring said armature and core means teeth into aligned relation and another winding on said pole pieces to produce a magnetic flux across said peripheral air gaps alone and switch magnetic flux from said radial to said peripheral air gaps.
 7. The invention as defined in claim 6 characterized by at least one of said projecting armature portions being disposed to so move relative to its associated pole piece as to reduce the overlapping area of said projecting portion and said pole piece as the length of the air gap therebetween diminishes.
 8. The invention as defined in claim 6 characterized by a plurality of said core means and associated rotatable armatures being positioned in side-by-side relation with the actuator extensions disposed alternately in opposed relations.
 9. The invention as defined in claim 8 characterized by the winding producing magnetic flux through both the radial and peripheral air gaps being common to a plurality of said core means in side-by-side relation, while the windings producing magnetic flux across only the peripheral air gaps are individual to each armature.
 10. The invention as defined in claim 9 characterized by said plurality of magnetic core means being joined by a molded plastic means bonded to all of said core means. 